This object reports the last quality level value actually received from a specific T4-table candidate source before any local override is applied, the raw received value mirroring cnsInpSrcQualityLevelRx but scoped to T4 selection candidates. Comparing this against the effective cnsT4ClkSrcQualityLevel for the same source tells an admin whether a local configuration is currently overriding what that candidate is genuinely advertising for T4 purposes. A sudden received QL drop here specifically on a T4 candidate, while the same physical link's T0 equivalent still looks fine, would suggest a T4-specific signaling issue rather than a physical link problem.